Embodiment
Describe specific implementation of the present utility model in detail below with reference to accompanying drawing.
As shown in Figure 1, the drive circuit of a kind of synchronous rectifier that the utility model provides, it mainly comprises following two parts:
1, turn-offs pre-process circuit 300, be used for obtaining detection signal, and this signal is compared with the first normal voltage V1, result from pre-cut-off signals from the drain electrode of synchronous rectifier T1;
2, cross zero balancing amplifying circuit 100, it links to each other with the output that turn-offs pre-process circuit 300, be used to gather the source signal of described synchronous rectifier T1, and this signal compared with the second normal voltage V2, during the voltage sum, the conducting of output synchronous rectifier T1 drives the signal of telecommunication makes synchronous rectifier T1 be in saturation condition between described source signal is greater than described normal voltage V2 and drain-source; Between described source signal is less than described normal voltage V2 and drain-source during the voltage sum, and when receiving described pre-cut-off signals by control end, the pre-pre-shutoff of turn-offing of output synchronous rectifier T1 drives the signal of telecommunication makes described synchronous rectifier T1 be in unsaturated state, comprises off state or magnifying state.
Compared with prior art, the utility model was by realizing collection to the source signal of synchronous rectifier T1 from increasing zero balancing amplifying circuit 100, and acquisition corresponding driving signal, in order to guarantee that circuit can be stably turn-offs rapidly when the current over-zero, then also increase by one and turn-offed pre-process circuit 300, be used to produce pre-cut-off signals, the controlling and driving signal makes synchronous rectifier T1 be in unsaturated state, comprises off state or magnifying state.
As shown in Figure 1, the shutoff pre-process circuit 300 here comprises: comparator A2, integrating capacitor C2, and integrating resistor R1, the end of integrating resistor R1 is used to connect the drain electrode of synchronous rectifier T1, the other end of integrating resistor R1 connects the end of integrating capacitor C2 and the input of comparator A2, another termination signal ground of integrating capacitor C2, another input of comparator A2 connects signal ground by the second normal voltage V2, and the output of comparator A2 is used to export described pre-cut-off signals.
For the stability of circuit, in described shutoff pre-process circuit 300, also comprise: be connected on the drain electrode of synchronous rectifier T1 and the capacitance C1 between the integrating resistor R1.
In order to limit the size of current of described pre-cut-off signals, in described shutoff pre-process circuit 300, also comprise: the output and the described current-limiting resistance R2 that crosses between the zero balancing amplifying circuit 100 that are connected on described comparator A2.
In view of shutoff pre-process circuit 100 structures shown in Figure 1, for integrating capacitor C2 is resetted, described drive circuit also comprises: the integrating capacitor reset circuit 400 that links to each other with described shutoff pre-process circuit 300 outputs, be used for when the described pre-cut-off signals of described shutoff pre-process circuit 300 outputs, described integrating capacitor C2 being resetted.Shown in Figure 1, integrating capacitor reset circuit 400 comprises: inverter ic 1, with door IC2 and switch element IC3, the output of described comparator A2 connects an input described and door IC2 by inverter ic 1, the output of described comparator A2 connects another input described and door IC2, described output with door IC2 is connected the control end of described switch element IC3, described switch element IC3 is connected in parallel on the two ends of described integrating capacitor, when described comparator A2 exported described pre-cut-off signals, described switch element IC3 closure made described integrating capacitor C2 discharge reduction.Here the switch element IC3 that is carried can be triode T31, a diode D31 in parallel between its collector and emitter, as shown in Figures 2 and 3.
As shown in Figure 1, the above-mentioned zero balancing amplifying circuit 100 of crossing comprises: controlled relatively amplifying unit A1, and the first normal voltage V1, the control end of described controlled amplifying unit A1 connects the output of described shutoff pre-process circuit 300, the described controlled relatively input of amplifying unit A1 is used for connecting by the first normal voltage V1 drain electrode of described synchronous rectifier T1, and described controlled relatively another input of amplifying unit A1 is used to connect the source electrode of described synchronous rectifier T1.In addition, if controlled amplifying unit A1 adopts operational amplifier, then increase impedance Z and realize negative feedback.
As shown in Figure 1, the first normal voltage V1 can adopt DC power supply, but Fig. 3 gives the realization circuit of the another kind of first normal voltage V1, it comprises: resistance R 12, diode D12, diode D13, triode T12, resistance R 11, DC power supply VCC, the negative electrode of diode D12 connects the base stage of triode T12, the emitter of triode T12 connects the source electrode of described synchronous rectifier T1 by resistance R 11, the anode of diode D12 and diode D13 is connected the output of DC power supply VCC by resistance R 12, and the negative electrode of diode D13 connects the described controlled relatively input of amplifying unit A1.In addition, as shown in Figure 1, controlled relatively amplifying unit A1 adopts controlled high speed operation amplifier, and as shown in Figures 2 and 3, controlled relatively amplifying unit A1 comprises triode T11, capacitor C 11, and capacitor C 11 is connected in parallel between the collector and emitter of triode T11, and the base stage of triode T11 links to each other with the negative electrode of diode D13, the emitter of triode T11 connects the source electrode of described synchronous rectifier T1, and the collector electrode of triode T11 connects the output of described shutoff pre-process circuit 300.In order to overcome the error that element device parameter matching causes, in Fig. 3, increased element D12 and D13, element D12 and element D13, elements T 12 is consistent with the T13 parameter, thereby complementary, has overcome the conforming problem that component parameters error and variations in temperature cause.
In order to increase driving force, described drive circuit also comprises: be connected on the power amplification circuit 200 between the described grid of crossing zero balancing amplifying circuit 100 outputs and synchronous rectifier T1.Its complementary output level that can adopt triode to constitute realizes 200 parts as shown in Figures 2 and 3.As shown in Figure 2, power amplifying part is made of compound transistor T21, T22 and triode T23, and its input links to each other with the collector electrode of triode T11, and output is connected with the control grid of synchronous rectifier T1, it is an electric current driving amplifier, and output voltage equates with input voltage.
With Fig. 2 and two given specific embodiments of Fig. 3, operation principle of the present utility model is described below.
As shown in Figure 1, illustrate that with the continuous current mode circuit of reversed excitation its basic principle is as follows:
1. turn-off the preliminary treatment circuit in advance: establish circuit and reached stable state, institute's charging voltage is last negative just down on the capacitance C1, and its voltage equals electric power output voltage, and it is zero that the voltage on the integrating capacitor C2 has been put.It is disconnected that the transformer secondary output coil is in the beginning rank that reset, at this moment, because of the appearance value of capacitance C1 appearance value much larger than integrating capacitor C2, can think that the voltage of capacitor C 1 is constant substantially, the resetting voltage of coil 1 charges to integrating capacitor C2 by resistance, after reseting procedure was finished, the electric capacity of capacitor C 2 was charged to certain value.At this moment, coil voltage overturns, coil begins discharge through synchronous rectifier to capacitor C 3, simultaneously, integrating capacitor is also discharged to coil L by integrating resistor R1, since inductance to discharge and recharge weber value equal, also equate and be worth the ampere-second of capacitor charge and discharge, obviously, when coil discharge finishes when entering next switch periods, voltage on the integrating capacitor C2 is also put and is 0V, has inserted a reference voltage V 2 on comparator A2, by the comparison of voltage on the integrating capacitor C2 and reference voltage V 2, thereby drawn pre-cut-off signals, this signal is reflected in the output of comparator A2 and is: when the voltage on the integrating capacitor C2 is lower than the voltage of reference voltage source V2, be output as low level, electric current flows into common ports from controlled output voltage amplifier through resistance R 2, then controlled operational amplifier A 1 is output as a low voltage, synchronous rectifier T1 breaks away from the saturation region and enters the amplification region, prepares for next step shutoff, has finished pre-shutoff.
2. current over-zero compares amplifying circuit: the negative terminal at the controlled output voltage high speed operation amplifier of element A1 connects the drain electrode that is connected to synchronous rectifier T1 through a reference voltage source V1, the source electrode that just is connected to synchronous rectifier T1 of element A1.
(1) opens the stage, when transformer time limit winding L begins to discharge, its polarity is last negative just down, diode current flow in the synchronous rectification body, its drain voltage hangs down about 0.7V approximately than source voltage, because the voltage of reference voltage source V1 is far below 0.7V, at this moment, operational amplifier A 1 is output as high level, and output also is high level after power discharge device 200 amplifies, and homogeneous tube T1 is open-minded synchronously.
(2) open the maintenance stage, after synchronous rectifier T1 opens, because the voltage Vsd on the synchronous rectifier still is higher than the voltage of joining voltage source V 1, operational amplifier A 1 is output as high level, and this process lasts till that always comparator A2 provides till the pre-cut-off signals.
(3) pre-turn off process, when transformer secondary output coil L discharge process closes to an end, comparator A2 output low level, the Control current of operational amplifier A 1 flows back to common port through resistance R 2, operational amplifier A 1 controlled signal, output voltage is reduced to about 4V, after power amplifier 200 amplified, synchronous rectifier T1 voltage reduced, and broke away from saturation condition, enter magnifying state, because the threshold values shutoff voltage of synchronous rectifier T1 is about 3V, that is to say that the control pole tension of synchronous rectifier T1 only need reduce 1V more just can enter off state, obviously, reducing to 3V with respect to traditional control pole tension from about the 10V just turn-offs then and can shorten the turn-off time greatly.
(4) the dynamic conducting resistance adjustment of synchronous rectifier rank are disconnected, when power source loads is light, because the discharging current of secondary coil L is less, synchronous rectifier T1 after opening soon its tube voltage drop Vsd just less than the voltage of reference voltage source V1, the output voltage of operational amplifier A 1 reduces, force the Vgs voltage of synchronous rectifier T1 to descend, the on state resistance of synchronous rectifier T1 increases, make its Vsd voltage rise, because the negative feedback of impedance network Z, make the output voltage of operational amplifier A 1 finally reach stable state at the voltage Vsd of synchronous rectifier T1 when equaling the voltage of reference voltage source V1, this process is a lasting adjustment process.When power source loads is heavier, this adjustment process is then very of short duration, because this moment, the discharging current of secondary coil L was bigger, voltage drop Vsd on the synchronous rectifier T1 is always greater than the voltage of reference voltage source V1, open up to the primary switch pipe, secondary coil L electric current descends rapidly, and as the pressure drop Vsd of synchronous rectifier T1 during less than the voltage of reference voltage source V1, adjustment process begins.
(5) synchronous rectifier current over-zero turn off process, when secondary coil L discharge stream constantly is reduced to zero, the dynamic conducting resistance of synchronous rectifier T1 is adjusted the disconnected end in rank, output capacitance C3 begins to discharge to secondary coil L through synchronous rectifier T1, because counter-rotating has taken place in electric current, under the effect of impedance network Z, the course of work of comparator A2 is a strong positive feedback process, promptly the voltage drop Vds owing to synchronous rectifier T1 constantly raises, the output voltage of operational amplifier A 1 then constantly reduces, corresponding with it synchronous rectifier T1 control pole tension Vgs also constantly reduces, the conducting resistance of synchronous rectifier T1 also constantly increases, the then corresponding rising of its pressure drop Vds, so process is a positive feedback process, synchronous rectifier T1 turn-offs rapidly.Secondary coil L enters reseting procedure, enters next switch periods.Need to prove at this, when the electric current of synchronous rectifier T1 arrives zero, corresponding with it synchronous rectifier T1 control pole tension should corresponding effect through operational amplifier A 1 adjust to zero, promptly reach shutoff, because in the process of big electric current continuous operation, di/dt is bigger, electric current is very of short duration to zero this process from big electric current, and the regular hour is wanted in the shutoff of synchronous rectifier T1, so just turn-off this process after zero passage is arranged, and because pre-effect of turn-offing the preliminary treatment circuit, it is also very of short duration to turn-off this process after the synchronous rectifier T1 zero passage, reverse current is less, and only for using the reverse recovery current level of Schottky as rectification circuit, detailed process can be referring to oscillogram shown in Figure 4 in actual measurement.From the whole process of circuit, there is not synchronous rectifier to close this process of diode current flow in the synchronous rectifier body of having no progeny, shown in Fig. 4 (b), therefore do not need to solve the recovery problem that diode current flow brought in the synchronous rectification body for synchronous rectifier Schottky in parallel.
3. integrating capacitor reset circuit: when dynamic load is worked, can accurately provide pre-cut-off signals in order to ensure this circuit, therefore will guarantee to start from scratch, discharge into zero and finish in each switch periods integrating capacitor charging voltage.When secondary coil L discharge process will finish, voltage on the integrating capacitor C2 progressively reduces and approaches zero, and less than reference voltage V 2, comparator A2 is output as low level, behind reverser IC1, be output as high level send into the door IC2 an input, at the voltage identical with synchronous rectifier Vgs with the voltage that another input inserted of door IC2, because secondary discharge also end this moment, the Vgs of synchronous rectifier is a high level signal, so IC2 exports a high level signal at this moment with door, the electronic switch IC3 that resets opens after the secondary coil discharge process finishes, synchronous rectifier T1 turn-offs, its Vgs voltage is zero, be low level promptly with door IC2 one input terminal voltage, with the output voltage of door IC2 be low level also, the electronic switch IC3 that resets turn-offs, finished the resetting of integrating capacitor C2, integrating capacitor enters next switch periods integral process.
As shown in Figure 2, relatively amplifying circuit 100 can also be by resistance R 11 for the synchronous rectifier current over-zero, resistance R 12, resistance R 13, capacitor C 11, diode D11 and triode T11 constitute, wherein resistance R 12 provides a reference current, this electric current R11 that flows through produces a reference voltage, the junction voltage of diode D11 equates with the BE junction voltage of triode T11, when big electric current is flowed through synchronous rectifier, its Vsd is far above the voltage of R11, the reference current that provides through resistance R 11 is all through diode D11, resistance R 12 flows into the drain electrode of synchronous rectifier, no current flows through in the BE knot of triode T11, triode ends, so the Vgs of synchronous rectifier T1 obtains a high voltage, synchronous rectifier T1 conducting.When the current over-zero of the synchronous rectifier T1 that flows through, its pressure drop Vsd also is 0V, so 1/2 BE that flows through triode T11 of the reference current that R12 produced ties triode T11 saturation conduction, thereby the Vgs voltage of synchronous rectifier T1 is pulled to end level, and synchronous rectifier T1 ends.When the electric current that flows through synchronous rectifier T1 hour, the voltage drop that produces on synchronous rectifier T1 is less, be Vsd less than the pressure drop of resistance R 11 but greater than zero, then the reference current of resistance R 12 generations has small part to flow through the BE knot of triode T11, triode T11 is in magnifying state, thereby the Vgs voltage of adjusting synchronous rectifier T1 reduces, the corresponding increase of its conducting resistance, make Vsd increase, maintain the voltage levvl of resistance R 11, this process is a lasting adjustment process, and capacitor C 11 is used to eliminate the vibration that is in course of adjustment and produces.The pre-preliminary treatment circuit that turn-offs is made of capacitance C1, integrating resistor R1, integrating capacitor C2, reference voltage V 2, OC door output comparator A2 and resistance R 2.When comparator A2 obtained pre-cut-off signals and is output as a low level, resistance R 13 constituted the dividing potential drops relation with resistance R 2, thereby had dragged down the output voltage of power amplifier.
Illustrating of above-mentioned each concrete steps is comparatively concrete; can not therefore think restriction to scope of patent protection of the present utility model; above-mentioned pre-shutoff preliminary treatment circuit, integrating capacitor reset circuit, current over-zero comparison amplifying circuit, power amplification drive circuit all can adopt above-mentioned each circuit; perhaps its variant, scope of patent protection of the present utility model should be as the criterion with claims.